COUP-TF plays a dual role in the regulation of the ovalbumin gene

The ovalbumin (Ov) gene contains a number of regulatory elements that contr ol its transcriptional activity and restrict expression to avian oviduct. O ne major regulatory region, the steroid-dependent regulatory element (SDRE) , is required for induction by estrogen and corticosterone. Another region, the negative regulatory element (NRE), downstream of the SDRE, acts primar ily to repress gene expression. In addition, experiments within indicate th at the binding site for the COUP transcription factor (COUP-TF) is also req uired for Ov gene transcription. To examine the interactions involving the SDRE, the NRE, and the COUP binding sites on Ov gene transcription, mutatio ns in these regions were made and transfected into primary oviduct cell cul tures. These experiments show that without the NRE, the SDRE is sufficient for induction by estrogen and corticosterone, irrespective of the COUP site . However, with the NRE intact, the COUP site is required for steroid induc tion, although without the NRE, the COUP site attenuates transcriptional ac tivity. More interestingly, overexpression of COUP-TF1 with the Ov wild-typ e reporter construct alleviates the requirement for steroid hormones. These results demonstrate that the COUP site is essential and has a dual role in Ov gene transcription and that steroid hormones might directly or indirect ly regulate the activity of COUP-TF1.